what to do with a Graupner sp 700bb 12v? - RC Groups
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Nov 26, 2002, 01:09 AM
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what to do with a Graupner sp 700bb 12v?

I got one of these cheap from HL and have no idea what to do with it. HL claims it will spin a 12x8 350+ whatts 25 amps on 12 cells direct drive. The motor is about 12oz, if I used the 4/5 A 1950 nimhs, another 17 or 18 oz. Any ideas? HL says about 35 oz of thrust. I was thinking about a Sureflite Cub or maybe a Big T on the above setup.
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Nov 26, 2002, 03:49 AM
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vintage1's Avatar
With a gearbox, and that sort of cell count or a few more on big props it will lift a 40 sized plane quite well. DD its OK for a faster type 25 warbird or something.

If you narrow down the plane type and post sizes and weights, we can plug in motocalc for you...
Nov 26, 2002, 02:46 PM
Registered User
How about the Easybuilt Hurricane I'm just finishing? 50" wingspan, fully sheeted about 410 sq inches, without drive and batteries 32 oz (w/radio gear). The motor I was considering was a MM/3:1-10cells.
Nov 26, 2002, 04:57 PM
Our Daddy and Heli Junkie
Fred Bronk's Avatar
If you stick with 3/4 SC CP1700 cells, it will work on the Hurricane, but it will be fast!

I like the MM setup, but a 2.5 ratio is much better to keep the prop to 11 inches.
Nov 26, 2002, 06:02 PM
Registered User
I like the cp1700's, but twelve of them would would be close to 20 oz. On paper, the Gr 700 would put out more watts (350) on 12c than the MM geared 3.5 on 10cells and both should put out around 35 oz thrust with 12" prop. BTW, can someone explain to me which is more important? how can both motors put out about the same thrust but the sp700 have far more watts? what the difference when botha er spinning the same prop?
Nov 26, 2002, 07:10 PM
Rehab is for quitters
LuckyArmpit's Avatar
I got one of these as well. Paid about $5 for it. I'm thinking of gearing it 3 to 1 or 3.5 to 1 and throw a big prop. Something like a large trainer weighing in around 60 to 70 oz. Big wingspan like
60 inches or so. Hehe, a flying Rhino!!!

Nov 27, 2002, 11:54 AM
Registered User
splat man,

That 350W figure is Watts IN. Propeller size and RPM indicate Watts out. If both motor setups spin the same prop at the same RPM, then the Watts out is the same on both. This is where efficiency comes into play. The one that requires less Watts in is more efficient.

The big Speed 700 is not as efficient in direct drive as the geared MM. If you put a gearbox and a big prop on the 700 and let 'er wind up, you'll get a whole lot more Watts out.
Nov 27, 2002, 12:12 PM
SEFF Contest Director
rcjunkie's Avatar
The best use! Paper Weight like all my Speed 600 motors!
Nov 27, 2002, 01:38 PM
Registered User
Mkirsh1- Thanks for the explanation--I always wondered about the "watts at prop" ratings some motors used.

Rcjunkie-- I know how you feel. This motor is a step up from the 600 can as far as quality. I have a bunch of various 550/600 can motors that are a real challenge to do anything with. Something that wieghs 8 oz yet puts out as much as a sp400g is a tough. I do think that a WWI 45-50" fighter that is LIGHT might work with this sp 700 geared at 2:1 swinging a 16" prop on 16 cells.